271 lines
8.2 KiB
C++
271 lines
8.2 KiB
C++
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/*
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* jddctmgr.c
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*
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* Copyright (C) 1994-1995, Thomas G. Lane.
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* This file is part of the Independent JPEG Group's software.
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* For conditions of distribution and use, see the accompanying README file.
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*
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* This file contains the inverse-DCT management logic.
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* This code selects a particular IDCT implementation to be used,
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* and it performs related housekeeping chores. No code in this file
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* is executed per IDCT step, only during output pass setup.
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*
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* Note that the IDCT routines are responsible for performing coefficient
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* dequantization as well as the IDCT proper. This module sets up the
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* dequantization multiplier table needed by the IDCT routine.
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*/
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#define JPEG_INTERNALS
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#include "jinclude.h"
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#include "jpeglib.h"
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#include "jdct.h" /* Private declarations for DCT subsystem */
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/*
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* The decompressor input side (jdinput.c) saves away the appropriate
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* quantization table for each component at the start of the first scan
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* involving that component. (This is necessary in order to correctly
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* decode files that reuse Q-table slots.)
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* When we are ready to make an output pass, the saved Q-table is converted
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* to a multiplier table that will actually be used by the IDCT routine.
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* The multiplier table contents are IDCT-method-dependent. To support
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* application changes in IDCT method between scans, we can remake the
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* multiplier tables if necessary.
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* In buffered-image mode, the first output pass may occur before any data
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* has been seen for some components, and thus before their Q-tables have
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* been saved away. To handle this case, multiplier tables are preset
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* to zeroes; the result of the IDCT will be a neutral gray level.
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*/
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/* Private subobject for this module */
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typedef struct {
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struct jpeg_inverse_dct pub; /* public fields */
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/* This array contains the IDCT method code that each multiplier table
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* is currently set up for, or -1 if it's not yet set up.
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* The actual multiplier tables are pointed to by dct_table in the
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* per-component comp_info structures.
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*/
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int cur_method[MAX_COMPONENTS];
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} my_idct_controller;
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typedef my_idct_controller * my_idct_ptr;
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/* Allocated multiplier tables: big enough for any supported variant */
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typedef union {
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ISLOW_MULT_TYPE islow_array[DCTSIZE2];
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#ifdef DCT_IFAST_SUPPORTED
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IFAST_MULT_TYPE ifast_array[DCTSIZE2];
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#endif
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#ifdef DCT_FLOAT_SUPPORTED
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FLOAT_MULT_TYPE float_array[DCTSIZE2];
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#endif
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} multiplier_table;
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/* The current scaled-IDCT routines require ISLOW-style multiplier tables,
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* so be sure to compile that code if either ISLOW or SCALING is requested.
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*/
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#ifdef DCT_ISLOW_SUPPORTED
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#define PROVIDE_ISLOW_TABLES
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#else
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#ifdef IDCT_SCALING_SUPPORTED
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#define PROVIDE_ISLOW_TABLES
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#endif
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#endif
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/*
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* Prepare for an output pass.
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* Here we select the proper IDCT routine for each component and build
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* a matching multiplier table.
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*/
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METHODDEF void
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start_pass (j_decompress_ptr cinfo)
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{
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my_idct_ptr idct = (my_idct_ptr) cinfo->idct;
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int ci, i;
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jpeg_component_info *compptr;
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int method = 0;
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inverse_DCT_method_ptr method_ptr = NULL;
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JQUANT_TBL * qtbl;
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for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
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ci++, compptr++) {
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/* Select the proper IDCT routine for this component's scaling */
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switch (compptr->DCT_scaled_size) {
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#ifdef IDCT_SCALING_SUPPORTED
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case 1:
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method_ptr = jpeg_idct_1x1;
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method = JDCT_ISLOW; /* jidctred uses islow-style table */
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break;
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case 2:
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method_ptr = jpeg_idct_2x2;
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method = JDCT_ISLOW; /* jidctred uses islow-style table */
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break;
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case 4:
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method_ptr = jpeg_idct_4x4;
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method = JDCT_ISLOW; /* jidctred uses islow-style table */
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break;
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#endif
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case DCTSIZE:
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switch (cinfo->dct_method) {
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#ifdef DCT_ISLOW_SUPPORTED
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case JDCT_ISLOW:
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method_ptr = jpeg_idct_islow;
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method = JDCT_ISLOW;
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break;
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#endif
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#ifdef DCT_IFAST_SUPPORTED
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case JDCT_IFAST:
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method_ptr = jpeg_idct_ifast;
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method = JDCT_IFAST;
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break;
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#endif
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#ifdef DCT_FLOAT_SUPPORTED
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case JDCT_FLOAT:
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method_ptr = jpeg_idct_float;
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method = JDCT_FLOAT;
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break;
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#endif
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default:
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ERREXIT(cinfo, JERR_NOT_COMPILED);
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break;
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}
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break;
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default:
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ERREXIT1(cinfo, JERR_BAD_DCTSIZE, compptr->DCT_scaled_size);
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break;
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}
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idct->pub.inverse_DCT[ci] = method_ptr;
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/* Create multiplier table from quant table.
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* However, we can skip this if the component is uninteresting
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* or if we already built the table. Also, if no quant table
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* has yet been saved for the component, we leave the
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* multiplier table all-zero; we'll be reading zeroes from the
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* coefficient controller's buffer anyway.
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*/
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if (! compptr->component_needed || idct->cur_method[ci] == method)
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continue;
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qtbl = compptr->quant_table;
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if (qtbl == NULL) /* happens if no data yet for component */
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continue;
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idct->cur_method[ci] = method;
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switch (method) {
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#ifdef PROVIDE_ISLOW_TABLES
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case JDCT_ISLOW:
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{
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/* For LL&M IDCT method, multipliers are equal to raw quantization
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* coefficients, but are stored in natural order as ints.
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*/
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ISLOW_MULT_TYPE * ismtbl = (ISLOW_MULT_TYPE *) compptr->dct_table;
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for (i = 0; i < DCTSIZE2; i++) {
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ismtbl[i] = (ISLOW_MULT_TYPE) qtbl->quantval[jpeg_zigzag_order[i]];
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}
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}
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break;
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#endif
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#ifdef DCT_IFAST_SUPPORTED
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case JDCT_IFAST:
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{
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/* For AA&N IDCT method, multipliers are equal to quantization
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* coefficients scaled by scalefactor[row]*scalefactor[col], where
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* scalefactor[0] = 1
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* scalefactor[k] = cos(k*PI/16) * sqrt(2) for k=1..7
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* For integer operation, the multiplier table is to be scaled by
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* IFAST_SCALE_BITS. The multipliers are stored in natural order.
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*/
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IFAST_MULT_TYPE * ifmtbl = (IFAST_MULT_TYPE *) compptr->dct_table;
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#define CONST_BITS 14
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static const INT16 aanscales[DCTSIZE2] = {
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/* precomputed values scaled up by 14 bits */
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16384, 22725, 21407, 19266, 16384, 12873, 8867, 4520,
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22725, 31521, 29692, 26722, 22725, 17855, 12299, 6270,
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21407, 29692, 27969, 25172, 21407, 16819, 11585, 5906,
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19266, 26722, 25172, 22654, 19266, 15137, 10426, 5315,
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16384, 22725, 21407, 19266, 16384, 12873, 8867, 4520,
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12873, 17855, 16819, 15137, 12873, 10114, 6967, 3552,
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8867, 12299, 11585, 10426, 8867, 6967, 4799, 2446,
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4520, 6270, 5906, 5315, 4520, 3552, 2446, 1247
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};
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SHIFT_TEMPS
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for (i = 0; i < DCTSIZE2; i++) {
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ifmtbl[i] = (IFAST_MULT_TYPE)
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DESCALE(MULTIPLY16V16((INT32) qtbl->quantval[jpeg_zigzag_order[i]],
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(INT32) aanscales[i]),
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CONST_BITS-IFAST_SCALE_BITS);
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}
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}
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break;
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#endif
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#ifdef DCT_FLOAT_SUPPORTED
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case JDCT_FLOAT:
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{
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/* For float AA&N IDCT method, multipliers are equal to quantization
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* coefficients scaled by scalefactor[row]*scalefactor[col], where
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* scalefactor[0] = 1
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* scalefactor[k] = cos(k*PI/16) * sqrt(2) for k=1..7
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* The multipliers are stored in natural order.
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*/
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FLOAT_MULT_TYPE * fmtbl = (FLOAT_MULT_TYPE *) compptr->dct_table;
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int row, col;
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static const double aanscalefactor[DCTSIZE] = {
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1.0, 1.387039845, 1.306562965, 1.175875602,
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1.0, 0.785694958, 0.541196100, 0.275899379
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};
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i = 0;
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for (row = 0; row < DCTSIZE; row++) {
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for (col = 0; col < DCTSIZE; col++) {
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fmtbl[i] = (FLOAT_MULT_TYPE)
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((double) qtbl->quantval[jpeg_zigzag_order[i]] *
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aanscalefactor[row] * aanscalefactor[col]);
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i++;
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}
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}
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}
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break;
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#endif
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default:
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ERREXIT(cinfo, JERR_NOT_COMPILED);
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break;
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}
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}
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}
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/*
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* Initialize IDCT manager.
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*/
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GLOBAL void
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jinit_inverse_dct (j_decompress_ptr cinfo)
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{
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my_idct_ptr idct;
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int ci;
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jpeg_component_info *compptr;
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idct = (my_idct_ptr)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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SIZEOF(my_idct_controller));
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cinfo->idct = (struct jpeg_inverse_dct *) idct;
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idct->pub.start_pass = start_pass;
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for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
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ci++, compptr++) {
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/* Allocate and pre-zero a multiplier table for each component */
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compptr->dct_table =
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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SIZEOF(multiplier_table));
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MEMZERO(compptr->dct_table, SIZEOF(multiplier_table));
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/* Mark multiplier table not yet set up for any method */
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idct->cur_method[ci] = -1;
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}
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}
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